1. Field of the Invention
The present invention relates to a motor driving apparatus, and more particularly to a motor driving apparatus which stores regenerative electric power and discharges the stored power for use as a motor drive current in an accelerating drive of the motor.
2. Description of Related Art
In a motor driving apparatus, a large drive current for acceleration is caused to flow in motor acceleration (power ruining) period, and a regenerative current is generated in deceleration period. Thus, the motor driving apparatus must be designed by taking into account of a peak current in motor acceleration (power running) period, resulting in increased size and cost of the apparatus. The regenerative current generated in deceleration period is thermally consumed by a regeneration resistor, resulting in wasted energy loss. On the other hand, there is known a motor driving apparatus comprising regeneration control means for feeding a regenerative current back to an AC power source through a converter section, thereby avoiding wasteful consumption of the regenerative current.
For the purpose of effectively utilizing the regenerative current and leveling the drive current, there is another known invention (see JP 2000-141440A) comprising a capacitor connected to a DC link through which a converter section (rectifier circuit) for converting AC power to DC power is connected to an inverter section for converting DC power to AC power. In acceleration period, electric power stored in the capacitor is supplied to the inverter section, whereas a regenerative current is stored in the capacitor in deceleration period. Thus, the drive current is leveled and a wasteful consumption of regenerative current is prevented.
In the aforementioned motor driving apparatus having regenerative control function for feeding regenerative current back to AC power source, a voltage at the DC link connecting the converter section with the inverter section is detected, and regeneration control is started when the voltage at the DC link increases due to regenerative current to a predetermined regeneration control start voltage.
On the other hand, in a motor driving apparatus of the type as described in JP 2000-141440A, which comprises the capacitor such as condenser for storing the regenerative current and which operates, during motor acceleration, to discharge the power stored in the capacitor to supply a motor drive current through the inverter, the charging voltage of the capacitor becomes higher than the regeneration control start voltage for regeneration control function and hence the regeneration control operation is started, when the charging voltage is applied to the DC link to attempt to discharge the power from the capacitor upon motor acceleration. For this reason, the capacitor cannot be added to a motor driving apparatus having the regenerative control function.
Capacitance of a capacitor can be made smaller using a higher voltage for charging the capacitor to the same level of energy, thereby enabling to prepare an additional circuit including charging/discharging circuits with reduced size and cost. Thus, there is a merit in adding the capacitor to the motor control apparatus.